Early birds could achieve liftoff
Gliding from trees wasn’t necessary for flight evolution, analysis suggests
ALT LAKE CITY — Flying dinosaurs took off from the ground — no leap from the trees required.
Ancient birds and some nonavian dinosaurs used their wings and powerful legs to launch themselves into the air, a new analysis of 51 winged dinos suggests. Paleontologist Michael Habib of the University of Southern California in Los Angeles reported the findings October 26 at the annual meeting of the Society of Vertebrate Paleontology.
“That’s a big deal, because the classic idea was that early birds started out gliding between trees,” says Yale ornithologist Michael Hanson.
The origin of flight in birds is a sticky subject, says paleontologist Corwin Sullivan of the Chinese Academy of Sciences in Beijing. “There’s been a long-standing controversy over whether flight evolved from the ground up or the trees down.”
Traditionally, scientists have thought that early birds scrambled up trees to get an altitude assist. The birds would then start their flight with a jump, like a hang glider diving off a cliff. Over time, descendants of those gliding birds would have evolved larger wings and, eventually, the ability to flap. Flapping “means you can push yourself forward on your own power,” Habib said. That’s how modern birds fly.
But in recent years, several lines of evidence have begun to dismantle the trees-down approach to flight evolution. Birds descended from terrestrial animals, for one, not tree dwellers. Habib’s team wondered whether early birds needed an elevation boost from trees at all — perhaps they could take off directly from the ground.
He and colleagues examined 51 fossil specimens from 37 different winged dinosaur genera that lived from 150 million to 70 million years ago, from the Late Jurassic to Late Cretaceous epochs. The sample included both avian and nonavian dinosaurs.
The specimens all had stiff, flightlike feathers on their forelimbs. But not all animals with feathered wings can fly, Habib says. To figure out if his specimens once could, he and colleagues analyzed wing length, body mass and hind limb muscle power, among other fossil features. Dinos that could fly (by flapping their wings) had to have enough leg strength to propel them up and enough wing speed to carry them forward.
Just 18 specimens (representing nine of the 37 groups) had the right stuff to get off the ground: every one of the avian specimens in the sample, as well as a few of the nonavian dinos too, including a tiny, four-winged dinosaur called Microraptor.
“Little guys did well,” Habib says. “Anything over four to five kilograms was struggling.”
Whether the early fliers could sustain flight for long distances is a different ball game, Habib says. “But there’s a big difference between flying a little and not flying at all.”
Early flying dinosaurs may have burst off the ground to escape from predators. This bursting behavior could have set the stage for the powered flight systems of modern birds, Habib says. Quick, powerful takeoffs “put a premium on large wings, large flight muscles and really fast wings” — all characteristics of today’s best fliers.